@Override
public void createContents(Composite parent) {
Category[] supported = {WORKSPACE, DATE};
categoryProvider = new CategoryProvider(supported, DATE);
categoryProvider.addObserver(this);
contentProvider = new TreePathContentProvider(new SessionDataTreeBuilder(categoryProvider));
contentProvider.addObserver(this);
valueProvider = createValueProvider();
valueProvider.addObserver(this);
// The main label provider for the first column: